A known distribution roller of the above type is disclosed in SE-A-9102938-9. According to its construction, the inner cylinder comprising the conversion mechanism is, at opposite ends, provided with gables which are rotatably mounted in needle bearings outside a hollow axle. The axle, in the mounted form of the roller, is located at a central axis, the central axis is common for the two bearing units and is fixedly mounted in the stand of the machine at opposite ends. Outside the hollow axle, the casing is rotatably mounted in bearings in an axially fixed condition, the casing at one end having an external, eccentrically located gear rim with fewer cogs than a cooperating, internal gear rim on the inner cylinder. These two gear rims together form an eccentric gear that causes the rotational speed difference between the casing and the inner cylinder (more precisely, the casing rotates with a slightly higher speed than the inner cylinder).
The difference of rotational speeds, or the relative rotative motion, between the casing and the inner cylinder constitutes only a fraction, for instance a value within the range 1:10 to 1:60, of the true rotational speed of the roller cylinder during operation (1200 to 2000 rpm). At its opposite end, the casing has a circumferential, substantially sinusoidally curved groove in which a runner or follower operates. A ball bearing is provided, and the runner is connected with the inner cylinder. Jointly, the groove and the runner form a conversion mechanism which causes the inner cylinder, and thereby also the outer roller cylinder, to have a reciprocating axial motion when the casing rotates or turns relative to the inner cylinder, due to the eccentric gear. The interior of the inner cylinder, which is delimited by the gables, contains suitable lubricating means. In order to prevent the lubrication from forcing its way out and contaminating the machine and the paper web that passes through the machine, seals are arranged in the form of gasket rings which are placed outside the needle bearings and are in contact, with on one hand, the stationary hollow axle, and on the other hand with the pertaining cylinder gables.
The roller construction disclosed in SE-A-9102938-9 is advantageous insofar as its eccentric gear enables the inclusion of the desired motion conversion function and also in that the distribution rollers work with high rotational speeds. However, this construction is also associated with a number of disadvantages which make its practical use difficult. On such difficulty is due to the fact that the two bearing units are mounted on a common, relatively weak central axle, and not only with the outer gables of the inner cylinders, at a considerable distance from the sides of the machine stand from which the two opposite ends of the central axle are fastened. Therefore, in practice, the central axle tends to be subjected to a bending phenomena which make the needle bearings start to bind. Moreover, these needle bearings must simultaneously be capable of serving as radial and axial bearings in that they must on one hand, permit the inner cylinder to rotate with high speed (e.g. 2000 rpm) relative to the stationary hollow axle and on the other hand, permit an axial displacement of the inner cylinder forwards and rearwardly along the hollow axle. Therefore, it will be readily understood that even a small amount of bending of the central axle may quickly result in a binding phenomena, and damage to the needle bearings.
Another disadvantage is the necessity of using gasket rings which are submitted to frequent reoccurring axial motions at the same time as they function radially between an immovable component (the hollow axle) and a fast-rotating component (the inner cylinder). There are no seals accessible on the market which have a larger diameter and which are capable of simultaneously fulfilling these purposes in a satisfactory way. Therefore, leaks through the gasket rings may occur when the known roller has a large diameter.
Further, another shortcoming of the conventional roller is that it does not include any means for indicating malfunctions within the bearing units, at an early stage. There is thus a risk of sudden damage which could occur and which could easily lead to one or more adjacent rollers in the machine being damaged, if external arrangements are not provided for preventive purposes. Furthermore, the maximum load on the roller is restricted by the above mentioned sinusoidal groove and the runner serving as a carrier which serves to provide the required motion conversion function. For axial movements which are large relative to the diameter of the casing, an unfavourable motion pattern develops between the runner and the groove of the casing which results in an undesirable wear at high axial loads. In order to counteract this, relatively hard and difficult-to-machine materials should be used, which makes production expensive.